1. Field of the Invention
The present invention relates to an ethanol fuel which contains polyalkylene glycol compounds as an ignition-improving agent.
2. Background of the Related Art
In a diesel engine, the combustion air is compressed to about 40 bars, the air reaching a temperature sufficiently high to ignite the diesel oil which is being injected. For gas oil, the temperature of use is specified at 336.degree. C., and for kerosene at 295.degree. C. For anhydrous ethanol, the ignition temperature in air is specified at 558.degree. C., and in oxygen gas at 425.degree. C. Morover, the evaporation of ethanol corresponds to a cooling of air by about 125.degree. C. in a stoichiometric relationship between ethanol and air. Thus, because of the high ignition temperature of the ethanol, it is not possible to use pure ethanol as fuel in a conventional diesel engine.
One way of igniting the ethanol fuel is to provide the diesel engine with spark plugs, but this necessitates extensive modifications to the engine's construction. For conventional diesel engines, a so-called ignition-improving agent, i.e., an agent which serves to lower the ignition temperature of the fuel, has been added to the ethanol. The predominant ignition-improving agent is the group consisting of alkyl nitrates, and the most used substrance is 2-ethylhexyl nitrate, generally abbreviated EHN.
EHN, which has a rather strong and disagreeable odour, is toxic and can be hydrolyzed to nitric acid and 2-ethylhexanol when stored for long periods of time, especially at elevated temperature. The hydrolysis causes a marked lowering of the pH, implying a serious risk of corrosion. A further serious objection to EHN is that the substance contains nitrogen which may increase the emission of nitrogen oxides in the exhaust gases. Therefore, it is generally desirable that EHN and other nitrate-based ignition-improving agents be replaced by an agent which is less hazardous to the environment and has higher stability.
It is also known to add corrosion inhibitors and lubricants to fuels. German Patent Application A1, 3,628,504 describes a fuel mixture of hydrocarbons, an alcohol and a corrosion inhibitor in an amount of up to 5000 ppm. This inhibitor contains a surface active agent, e.g., block polymers of alkylene oxides.
British Patent Application A2, 143,846 discloses the use of 0.005-0.05% by weight of a polyalkylene glycol as a lubricity improver in a diesel fuel based on methanol and/or ethanol.